How do I transform triangle polygons into quads?
This can be done within 10 secs. I've seen this tutorial two years ago. I'm sure you can speed up the whole workflow with the new powerful tools developed since then. :) My suggestion for step 1 to 5 on this exercise can be seen below in briefly 3 steps. However, if you just want to focus on the exact question, just jump to Step 3:

P.S.: Since you said you are new to Blender, I tried to reproduce every detailed step, so it may look a bit long, but all operations can be done in a flash if you get it then.